Systems and methods for providing backup energy to a load

ABSTRACT

Backup energy systems utilizing compressed air storage (CAS) systems and bridging energy systems to supply backup power to a load are provided. During a power failure, the bridging energy system provides backup power to the load at least until the CAS system begins supplying adequate power. In various embodiments, backup power capability is enhanced through the use of one or more exhaustless heaters, which are used to heat compressed air. The compressed air, in turn, drives a turbine which is used to power an electrical generator. In various embodiments, ambient air heat exchangers or other types of heat exchangers are used to heat compressed air prior to the compressed air being routed to the turbine, thereby increasing system efficiency. Backup power and backup HVAC are also provided by utilizing turbine exhaust, heat exchangers and various resistive heating elements.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional of co-pending, commonly-assigned U.S. patentapplication Ser. No. 10/361,728, filed Feb. 5, 2003. This priorapplication is hereby incorporated by reference herein in itsentireties.

BACKGROUND OF THE INVENTION

This invention relates to backup energy systems for supplying backuppower to a load. More particularly, this invention relates to backupenergy systems that use the combination of a compressed air storage(CAS) system and an energy storage system, or bridging energy system, toprovide backup power to a load during a failure of a primary powersource.

CAS systems are well known. CAS systems use compressed air to drive aturbine, which in turn powers an electrical generator. Prior to reachingthe turbine, the compressed air may be heated using a suitable type offuel-combustion system. Alternatively, an exhaustless heater may be usedto heat the compressed air. This type of CAS, which uses an exhaustlessheater, is known as a combined thermal and compressed air storage(TACAS) system. Such systems are disclosed in a commonly-assigned,co-pending U.S. patent application Ser. No. 10/361,729, filed Feb. 5,2003, entitled “Thermal and Compressed Air Storage System,” now U.S.Pat. No. 7,086,231, which is hereby incorporated by reference in itsentirety.

When the turbine is driven by the compressed air, heated or not, theturbine powers an electrical generator that produces electrical power atan output. The use of CAS systems alone to provide backup power,however, is not practical in applications where, for example, even avery brief power outage to a load is detrimental. In CAS systems, theretypically is a slight delay because the rotor of the turbine must besped up before the turbine is able to power the electrical generator.This renders the use of CAS systems, by themselves, an unacceptablemanner in which to provide backup power in many applications.

Energy storage systems, on the other hand, provide substantiallyinstantaneous backup power to a load in the event of a primary powersource failure. An example of an energy storage system is a bank ofchemical batteries, which includes one or more chemical batteries. Inorder to maintain backup power capability, these batteries are eitherreplaced once drained or charged during normal operating conditions(e.g., when utility power is providing sufficient power). In the lattercase, the bank of chemical batteries is connected to a battery chargerwhich provides a trickle charge to keep the batteries energized duringnormal operating conditions. The energy stored in the chemical batteriesis then used to supply power to the load during a utility power failure.

Chemical batteries, however, suffer from various deficiencies, includingbulkiness, lack of reliability, limited lifespan, temperaturesensitivity, high maintenance costs and relatively low safety. Forexample, chemical batteries require relatively constant and complexrecharging, depending on the type of batteries involved, to insure thatthe batteries continue to operate efficiently and maintain their fullstorage capacity. Moreover, chemical battery banks must typically belocated in remote battery storage rooms which house the batteries, inpart due to safety considerations and bulkiness, and must be replacedapproximately every 3-8 years due to the limited lifespan of thebatteries. Additionally, high maintenance costs arise from the need toinstall special venting and air-conditioning systems for dedicatedbattery storage rooms.

Another commonly used type of energy storage system is a flywheel energystorage system. During normal operating conditions, a flywheel isrotated by the primary power source such that it stores kinetic energyin the form of rotational momentum (see, e.g., Clifton et al. U.S. Pat.No. 5,731,645, which is hereby incorporated by reference herein in itsentirety). When the primary power fails, the kinetic energy stored inthe flywheel is used to drive a generator, which provides the load withbackup power. Flywheel energy storage systems, however, are only capableof supplying backup power to the load for a relatively short period oftime (e.g., until the kinetic energy in the flywheel has been used up).Once the energy stored in the flywheel energy storage system isdepleted, backup power is no longer available for the critical load

Energy storage systems such as described above are often used inuninterruptible power supply (UPS) systems, which are used to ensurethat an interruption in power from the primary power source (e.g., autility power failure) does not lead to disturbance of the power beingsupplied to the critical load. UPS systems using flywheel energy storagesystems, for example, are described in Gottfried U.S. Pat. No.4,460,834. Alternatively, Pinkerton et al. U.S. Pat. No. 6,255,743describes a UPS system which utilizes a turbine energy storage system,while Pinkerton et al. U.S. Pat. No. 6,192,687 describes a UPS systemwhich utilizes a source of thermal energy to produce backup electricalpower.

Generally, when a critical load is being powered by utility power, knownUPS systems store energy in an energy storage system, or bridging energysystem. Thereafter, during a failure in utility power (i.e., when theutility power source is not able to provide power at a predeterminedquantity or quality level), these UPS systems begin supplying backuppower to the critical load using the energy stored in the energy storagesystem. Moreover, persons skilled in the art will appreciate that powerconditioning or other typical UPS features may be included to furtherenhance the ability to provide continuous power to the critical load.

The UPS systems described above, however, suffer from variousdeficiencies. Known flywheel-UPS systems, for example, have only alimited supply of backup energy. UPS systems using battery banks,moreover, are problematic because they suffer from over-temperatureconditions when utility power is not present to power heating,ventilation, and air conditioning (HVAC) systems.

In view of the foregoing, it is an object of this invention to providebackup energy systems which provide undisturbed power to a critical loadwhile eliminating problems associated with known backup energy systems.

SUMMARY OF THE INVENTION

These and other objects of the present invention are accomplished inaccordance with the principles of the present invention by providingvarious backup energy systems which utilize a combination of CAS systemsand energy storage systems. These energy storage systems function asbridging energy systems which supply energy between the time thatutility power fails and the CAS system begins supplying sufficient powerto the load.

In one embodiment, when utility power is available, it supplies power tothe critical load while also providing power that is stored in thebridging energy system (e.g., a flywheel energy storage system or achemical battery bank). Additionally, utility power drives a motor thatpowers a compressor to provide compressed air which is then stored in apressure tank. When utility power fails, the bridging energy systembegins providing power to the critical load. The bridging energy systemcontinues to provide power until compressed air from the pressure tankadequately drives the turbine, which powers a generator to provide powerto the critical load.

In a similar embodiment, utility power is used to heat the thermalstorage material of a thermal storage unit (TSU) which is added to theCAS system (to form a TACAS system). When utility power fails, thebridging energy system begins supplying power to the load. Compressedair from the pressure tank is then heated by the TSU, an exhaustlessheater, prior to the compressed air driving the turbine.

In another embodiment of the present invention, a fuel-combustion systemheats compressed air from the pressure tank before the compressed air isrouted to the turbine.

In other embodiments of the present invention, various integrated TACASUPS systems are used to provide uninterruptible power to a criticalload. Alternatively, additional types of exhaustless heaters, other thana TSU, may be included to further heat compressed air from the pressuretank before it is routed to the turbine.

In another embodiment of the present invention, a TACAS system is usedto provide backup HVAC in addition to backup power to a critical load,or critical electronics.

In other embodiments of the present invention, the compressor andpressure tank of the above described backup energy systems are replacedwith replaceable compressed air cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention, its nature andvarious advantages will be more apparent upon consideration of thefollowing detailed description, taken in conjunction with theaccompanying drawings, in which like reference characters refer to likeparts throughout, and in which:

FIG. 1A is a schematic diagram of a conventional CAS system;

FIG. 1B is a schematic diagram of a conventional flywheel backup energystorage system;

FIG. 1C is a schematic diagram of a conventional flywheel UPS system;

FIG. 2 is a schematic diagram of a conventional backup energy systemusing an HVAC system;

FIG. 3 is a schematic diagram of a backup energy system in accordancewith the principles of the present invention;

FIG. 4 is a schematic diagram of another backup energy system inaccordance with the principles of the present invention;

FIG. 5 is a schematic diagram of another backup energy system inaccordance with the principles of the present invention;

FIG. 6 is a schematic diagram of an integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 7 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 8 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 9 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 10 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 11 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 12 is a schematic diagram of another integrated TACAS UPS system inaccordance with the principles of the present invention;

FIG. 13 is a schematic diagram of a backup energy system for providingbackup power to a load while also providing backup HVAC in accordancewith the principles of the present invention;.

FIG. 14 is a schematic diagram of another backup energy system forproviding backup power to a load while also providing backup HVAC inaccordance with the principles of the present invention;

FIG. 15 is a schematic diagram of a simplified backup HVAC system inaccordance with the principles of the present invention;

FIG. 16 is a three-dimensional perspective view of a TACAS UPS system inaccordance with the principles of the present invention; and

FIG. 17 is a three-dimensional perspective view of another TACAS UPSsystem in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows a conventional CAS system for providing backup power to aload.

CAS system 100 includes a primary power source, utility input 110, thatprovides input power to motor 120, which may be any conventional type ofmotor (e.g., a rotary electric machine). Motor 120 is coupled tocompressor 122 such that when motor 120 is receiving input power fromutility input 110, it drives compressor 122. Compressor 122, when drivenby motor 120, supplies compressed air to pressure tank 126 through valve128. Compressor 122 may be any type of compressor which compacts orcompresses air (e.g., atmospheric air) to occupy a smaller space insideof pressure tank 126.

As shown in FIG. 1A, pressure tank 126 is coupled to compressor 122through valve 128. It should be understood, however, that pressure tank126 in CAS system 100, as well as the pressure tanks associated with theother systems described herein, may be replaced with any other suitabletype of air reservoir capable of storing compressed air. For example, anunderground salt dome (not shown) may be used in place of pressure tank126.

When CAS system 100 is to provide electric power, compressed air frompressure tank 126 is routed through valve 128 to drive turbine 130. Thecompressed air flows against the turbine rotor (not shown) of turbine130, which may be any suitable type of turbine (e.g., a radial-flowturbine). In turn, turbine 130 drives electrical generator 132, whichprovides power to critical load 140.

Moreover, as illustrated in FIG. 1A, turbine 130 releases exhaust air.The exhaust from turbine 130 may be vented through an exhaust pipe (notshown), or simply released to recombine with atmospheric air.

CAS system 100, however, has several deficiencies associated withproviding backup power to critical load 140. For example, once utilityinput 110 stops supplying sufficient power to critical load 140,compressed air from pressure tank 126 must be supplied to turbine 130for a short period of time before the turbine rotor is rotating at asufficient rate to allow turbine 130 to properly power electricalgenerator 132. This poor transient response can result in an inabilityto provide critical load 140 with an undisturbed supply of power onceutility input 110 stops providing sufficient power. Additionally, theduration of backup power provided by CAS system 100 is limited by theamount of compressed air in pressure tank 126. Once pressure tank 126 isdepleted, CAS system 100 cannot power critical load 140.

FIG. 1B shows a conventional flywheel backup energy storage system 150which provides backup power to critical load 140. Unlike CAS system 100described above, once utility input 110 ceases to provide sufficientpower to critical load 140, backup power is almost immediately availableto be supplied to critical load 140.

As illustrated in FIG. 1B, during normal operating conditions, utilityinput 110 supplies power to critical load 140 as well as to electricalmachine 154. At this time, electrical machine 154 operates as a motorand drives flywheel 152 such that it stores kinetic energy. Once utilitypower fails, flywheel 152 begins driving electrical machine 154, nowacting as a generator, to supply backup power to critical load 140.

Although the use of a flywheel such as shown in FIG. 1B largelyeliminates the problem of discontinuous power being supplied to criticalload 140, flywheel 152 is only able to drive electrical machine 154 fora relatively short period of time. After the kinetic energy in flywheel152 has been used, critical load 140 may become powerless if utilitypower has not yet returned.

FIG. 1C shows a conventional flywheel UPS system 160 which is similar tothe flywheel backup energy storage system 150 shown in FIG. 1B, althoughit also contains additional AC circuitry.

Flywheel UPS system 160 includes utility input 110. When utility input110 is supplying sufficient power, the AC power from utility input 110is fed into AC-to-DC converter 162 and converted to DC power. This DCpower, originating from utility input 110, is fed across DC buss 168 toDC-to-AC converter 164, which converts the DC power back to AC power tobe supplied to critical load 140. Converters 162 and 164, as well as theremainder of the converters described herein, may be provided asconventional converters, an array of high power semiconductor switches,or other suitable circuitry without departing from the principles of thepresent invention. For example, AC-to-DC converter 162 may be a simplerectifier circuit, or it may be any other conventional circuit thatconverts power from AC to DC. Also, for example, DC-to-AC converter 164may be a simple inverter circuit, or it may be any other conventionalcircuit that converts power from DC to AC.

While utility input 110 is supplying power, converter 166 converts DCpower from DC buss 168 to AC power which is provided to electricalmachine 154. At this time, electrical machine 154 (which, as explainedabove, can operate at different times as a motor or as a generator) isoperating as a motor and rotates flywheel 152 so that flywheel 152stores kinetic energy.

DC buss 168 is monitored by UPS control electronics (not shown), which,depending on the available source of power, controls whether criticalload 140 is supplied power from either utility input 110, flywheel 152or both. Once a utility power failure is detected, the kinetic energy offlywheel 152 is used to supply backup power to critical load 140. Atthis time, the kinetic energy of flywheel 152 is used to driveelectrical machine 154, now operating as a generator, to produce ACpower. This AC power is converted by converter 166 to DC power andsupplied to DC buss 168. Flywheel 152 continues to provide power to DCbuss 168 until either it is drained of power or until utility input 110resumes supplying adequate power to critical load 140, as determined bythe UPS control electronics (not shown). As with flywheel backup energystorage system 150, a significant limitation of flywheel UPS system 160is that flywheel 152 can store only a limited amount of energy toprovide backup power to critical load 140.

FIG. 2 shows a conventional backup energy system 200 using an HVACsystem 240 to maintain critical electronics being powered withinacceptable temperature limits. When operating normally, utility input110 supplies power to operate critical electronics 220 (e.g.,telecommunications electronics). At this time, utility input 110 alsosupplies power to HVAC system 240, which uses a conventional ambient airheat exchanger 250 in order to maintain the temperature within housing241 below a predetermined level.

Housing 241 also includes a bank of batteries 230 which suppliesshort-term backup power to critical electronics 220, through DC to ACconverter 231, when utility power 110 has failed. When utility input 110is not available to power HVAC system 240, however, backup energy system200 is prone to suffer from over-temperature conditions. Theseover-temperature conditions not only negatively impact the operation ofcritical electronics 220, but they further degrade the performance ofbattery bank 230. Such degradation in performance arises in the form ofa shortened duration for which battery bank 230 is capable of providingbackup power.

FIG. 3 shows a backup energy system 300 for providing backup power to aload in accordance with the principles of the present invention. Backupenergy system 300 and the other systems described below are shown toinclude several components which, as persons skilled in the art willappreciate, may be combined as desired in accordance with the principlesof the present invention without departing from the spirit of thepresent invention.

Backup energy system 300 includes utility input 310 which supplies powerto critical load 340 during normal operating conditions. Persons skilledin the art will appreciate that utility input 310 (or utility input 110described above) may be any suitable type of primary power source. Asillustrated in FIG. 3, backup energy system 300 also includes a bridgingenergy system 302 integrated with the components of a CAS system inorder to provide backup power to critical load 340. Backup energy system300 includes motor 320, compressor 322, pressure tank 326, valve 328,turbine 330 and electrical machine 332. Bridging energy system 302 maybe any suitable type of energy storage system capable of supplying ashort term backup supply of power (e.g., a flywheel energy storagesystem).

During normal operating conditions, utility input 310 supplies criticalload 340 with power. Utility power 310 also provides bridging energysystem 302 with power so that it can store energy to be used, forexample, during a power outage. Additionally, utility input 310 powersmotor 320 which drives compressor 322 such that compressed air is routedthrough valve 328 and stored in pressure tank 326. It should beunderstood that pressure tank 326 can be replaced by any other suitabletype of compressed air reservoir, such as an underground salt dome.

Compressor 322, meanwhile, can be any suitable type of compressor whichcompacts or compresses air (e.g., atmospheric air) to occupy a smallerspace inside of pressure tank 326. Valve 328 may be a conventional valveor any other suitable device for selectively permitting or preventingthe flow of air. Moreover, rather than using a single valve 328 todirect the flow of air from compressor 322 to pressure tank 326 and frompressure tank 326 to turbine 330, two separate valves may be used.

When there is a utility power failure, stored energy in bridging energysystem 302 is used to power critical load 340. Shortly after utilityinput 310 stops providing adequate power (e.g., after approximately afew seconds), valve 328 is opened so that compressed air is routed toturbine 330. It should be understood that turbine 330 may be any type ofconventional air turbine. For example, turbine 330 may be a radial-flowturbine, an impulse turbine or a reaction turbine. Turbine 330 in turnpowers electrical machine 332, acting as a generator, to provide powerto critical load 340. For a relatively short period of time, bothbridging energy system 302 and the components of the CAS system may beused to power critical load 340. After this short period of time (e.g.,less than approximately 10 seconds), the CAS system of backup energysystem 300 becomes the only source of power for critical load 340 untilutility power 310 returns. Moreover, during the time that the CAS systemis the sole supplier of power to critical load 340, bridging energysystem 302 begins to draw a small amount of energy from the output ofelectrical machine 332 as it recharges.

Persons skilled in the art appreciate that the response by turbine 330to step changes in the critical load 340 may be inadequate for certainapplications. Accordingly, bridging energy system 302, in addition toproviding power to critical load 340 until electrical machine 332 issupplying adequate power, preferably also compensates for step changesin the critical load 340. For example, bridging energy system 302 may beused to discharge or absorb energy during step changes in the criticalload 340 to ensure a continuous supply of power to the critical load340.

Persons skilled in the art will also appreciate that it is within thescope of the present invention to supply utility power in any of theembodiments described herein directly to electrical machine 332, whichcan be capable of operating at different times as a motor and agenerator. Moreover, when supplied with power from utility input 310 oranother power source, electrical machine 332 can operate as a motor todrive turbine 330 such that the turbine rotor (not shown) is constantlyrotated. In this manner, the transient response of turbine 330 may beimproved, thus allowing turbine 330 to also act as the bridging energysystem, providing substantially immediate backup power to critical load340 during a power failure. Accordingly, a separate bridging energysystem may not be necessary if the rotor of turbine 330 is continuouslyspinning when utility power 310 is available. It should be understood,however, that it may be preferable to conserve energy and not use powerfrom utility input 310 to maintain the rotation of the turbine rotor.Furthermore, although critical load 340 is shown as requiring AC power,the invention is not limited in this manner. In certain applications,critical load 340 may be DC electronics, in which case converters (notshown) may be used as necessary in order to supply DC power to criticalload 340 from any of the power sources described herein.

FIG. 4 shows another backup energy system 400 in accordance with theprinciples of the present invention. Backup energy system 400 is similarto backup energy system 300, except that backup energy system 400 alsoincludes an exhaustless heater, TSU 402. It will be understood bypersons skilled in the art that the term exhaustless heater as usedherein refers to any type of heater which does riot produce a wasteproduct (e.g., a noxious emission). Persons skilled in the art will alsoappreciate that that TSU 402 may be any suitable type of thermal storageunit, which can transfer heat from the thermal storage material (notshown) in TSU 402 to the compressed air coming from pressure tank 326(via valve 328) before the air is provided to turbine 330.

When utility input 310 is supplying power to critical load 340, it isalso used to heat the thermal storage material (not shown) of TSU 402 toat least a predetermined temperature. Persons skilled in the art willappreciate that the thermal storage material of TSU 402 may be heated byany suitable type of heating system. The thermal storage material of TSU402 may be heated, for example, by a resistive heater (not shown).Additionally, for example, a closed-loop pipe containing a working fluid(e.g., oil) that is heated may be used. In this case, the heated fluidpumped through a closed-loop pipe may be used to convey thermal energyto the working fluid (or other type of material) that makes up thethermal storage material of TSU 402. Alternatively, an induction heatermay be used to heat the thermal storage material of TSU 402.

As illustrated in FIG. 4, once backup power is needed, stored energy inbridging energy system 302 is used to power critical load 340. Shortlythereafter, compressed air is routed through TSU 402 such that thecompressed air is heated prior to entering turbine 330. The benefit ofheating compressed air from pressure tank 326 prior to being routed toturbine 330 is that less compressed air is required to produce the sameamount of electrical output from electrical machine 332.

As an alternative to using TSU 402, which requires an electrical powersource such as utility input 310 to maintain the temperature of thethermal storage unit therein, a fuel-combustion system can be used inaccordance with the principles of the present invention to heatcompressed air from pressure tank 326. FIG. 5 shows a schematic diagramof a backup energy system 500, which utilizes a fuel-combustion system502, for providing backup power to critical load 340. Backup energysystem 500 is substantially identical to backup energy system 400,except that TSU 402 has been replaced by fuel-combustion system 502.

When there is a utility power failure, bridging energy system 302provides substantially instantaneous backup power to critical load 340(as described above). Compressed air from pressure tank 326 is thenrouted through valve 328 to combustion system 502. Combustion system502, as illustrated in FIG. 5, receives a fuel input which is mixed withthe air being supplied through valve 328. Combustion system 502 ignitesand burns the fuel, and the resulting heated air is supplied to turbine330.

The hot air emerging from combustion system 502 flows against theturbine rotor (not shown) of turbine 330. Once driven by the heatedcompressed air, turbine 330 powers electrical machine 332 so thatelectrical machine 332 provides power to critical load 340.

FIG. 6 shows an integrated TACAS UPS system 600 for providing backuppower to a load during a utility power failure (e.g., during degradationin the power being supplied by the utility power source or a completeloss of utility power) in accordance with the principles of the presentinvention. While TACAS UPS system 600 and the other TACAS UPS systemsdescribed herein are capable of providing backup power during a loss ofutility power, the TACAS UPS systems may also provide backup power,power conditioning or other typical UPS features to the critical loadduring a degradation of the power (e.g., when the quality level of theutility power is not adequate). Persons skilled in the art willappreciate that during a short term degradation of the utility powersource, for example, bridging energy system 302 may provide temporarybackup power to critical load 340 without electrical machine 332 havingto come online.

In addition to the components found in backup energy system 400, TACASUPS system 600 also includes converters 602, 604, 606, and 608, DC buss603 and UPS control electronics 609. When utility input 310 is supplyingadequate power, the power from utility input 310 is supplied throughconverters 602 and 604, which precisely regulate the electrical outputthat is fed to critical load 340. It should be noted that although UPSsystems which convert AC power from a primary power source to DC powerand then back to AC power to be supplied to the load are explainedherein (these types of UPS systems are known as double-conversion UPSsystems), the invention is not limited in this manner. Other types ofUPS systems (not shown) such as line-interactive UPS systems or singleconversion UPS systems may be used without departing from the scope ofthe present invention.

Another converter 606 converts DC power from DC buss 603 to AC powerwhich is used to charge bridging energy system 302. Although converter606 is shown as a single converter capable of converting power from DCto AC and from AC to DC, such as other converters described herein, twoseparate converters may be used without departing from the scope of thepresent invention.

In addition to supplying power to critical load 340, the output ofDC-to-AC converter 604 is used to supply power to motor 320 and TSU 402as illustrated in FIG. 6. Although, it should be understood by thoseskilled in the art that utility input 310 can directly supply power tomotor 320 or TSU 402 without departing from the scope of the presentinvention.

When motor 320 is receiving power from primary power source 310, motor320 drives compressor 322, which supplies compressed air through valve328 to pressure tank 326. As explained above, pressure tank 326 can beany suitable type of air reservoir capable of storing compressed air,such as an underground salt dome.

During a power failure, the energy stored in bridging energy system 302is used to power DC buss 603, through converter 606, for a relativelyshort period of time (e.g., up to approximately 2-5 seconds). Shortlyafter utility input 310 has failed (e.g., after approximately a fewseconds), valve 328 is opened such that compressed air is heated by TSU402, and routed to turbine 330. Turbine 330 is then driven by the heatedcompressed air from pressure tank 326, and in turn, powers electricalmachine 332 (which is acting as a generator) to provide AC power.Converter 608 converts the AC power coming from electrical machine 332to DC 30 power to supply DC buss 603. For a relatively short period oftime, both bridging energy system 302 and the output of converter 608are used to power critical load 340, through DC-to-AC converter 604.After this short period of time (e.g., less than approximately 10seconds), the TACAS system of TACAS UPS system 600 becomes the onlysource of power for critical load 340, until utility power has returned.During the time that the TACAS system is the sole supplier of power,bridging energy system 302 begins to draw a small amount of energy fromthe output of converter 608 as it recharges.

As also shown in FIG. 6 by dotted line 614, relatively cool air emergingfrom turbine 330, exhaust 612, is optionally used to cool the variousconverters and other components of TACAS UPS system 600. Althoughexhaust 612 is generally warmer than normal ambient air, this air isgenerally cool relative to the various components in TACAS UPS system600, and therefore, can provide some cooling to these components. Coolair from pressure tank 326 may also be used to cool these componentsbefore it is routed to TSU 402. Alternatively, exhaust 612 may be ventedelsewhere through an exhaust pipe (not shown), or simply released torecombine with atmospheric air. The invention is not limited in thismanner.

When utility power 310 returns and converter 602 is again routing powerto DC buss 603, converter 608 stops routing power to DC buss 603. Atthis time, TSU 402 and motor 320 start drawing power from utility input310 to heat the thermal storage material of TSU 402 back up to at leastthe predetermined temperature level and to refill pressure tank 326 withcompressed air.

It should further be understood by those skilled in the art that asingle controller such as UPS control electronics 609 may be used tocontrol the various components and switches (not shown) in order todirect the flow of power from the appropriate power source to criticalload 340. Moreover, although only shown in TACAS UPS system 600, UPScontrol electronics 609 may be included in any of the backup energysystems presented in accordance with the principles of the presentinvention.

UPS control electronics 609 monitors DC buss 603 using a sense line (notshown). Upon detecting a power failure, trigger signals (not shown) aresent to various components in TACAS UPS system 600 to ensure acontinuous power supply to critical load 340. Alternatively, UPS controlelectronics 609 may also sense the input to converter 602 or the outputof converter 604 without departing from the scope of the presentinvention. Furthermore, both the TACAS and UPS elements can be locatedin a single housing and share components (e.g., cooling fans, powersupplies or a user display), thereby saving money and making TACAS UPSsystem 600 more compact.

Another TACAS UPS system 700 is illustrated in FIG. 7. TACAS UPS system700 utilizes many of the components found in TACAS UPS system 600, withthe primary difference between the two being that TACAS UPS system 700utilizes a turbine exhaust heat exchanger 712. Turbine exhaust heatexchanger 712 uses exhaust 612 emerging from turbine 330 to pre-heat thegenerally below ambient temperature compressed air from pressure tank326 before it is routed to TSU 402. This may result in a slightly largerand more complex system than TACAS UPS system 600, however, TACAS UPSsystem 700 also reduces the amount of thermal storage material necessaryin TSU 402 for a given energy output, and also increases system “roundtrip” efficiency (defined as the electrical energy output divided by theelectrical energy input of the system). This configuration also coolsexhaust 612 from turbine 330 by drawing heat away, which can beimportant for indoor applications (e.g., applications which typicallyrender a room too hot for occupancy).

Additionally, in TACAS UPS system 700, bridging energy system 302 isreplaced by flywheel 702 and electrical machine 704. It should beunderstood, however, that other types of energy storage systems may beused in TACAS UPS system 700 and the remainder of the systems describedherein. As illustrated in FIG. 7, when utility input 310 is supplyingpower, DC power from DC buss 603 is converted to AC power by converter606. This AC power drives electrical machine 704, which in turn drivesflywheel 702 to store kinetic energy in the form of rotational momentum.Alternatively, primary utility input 310 can be made to directly powerelectrical machine 704 without departing from the scope of the presentinvention. In the event of a utility power failure, flywheel 702 andelectrical machine 704, now acting as a generator, use stored kineticenergy to supply DC buss 603 with power until the TACAS system beginssupplying adequate power (at which time flywheel 702 begins to rechargeits stored kinetic energy as described above).

FIG. 8 shows TACAS UPS system 800 which includes many of the samecomponents found in TACAS UPS system 700 of FIG. 7, except that TACASUPS system 800 does not use motor 320, compressor 322 or pressure tank326. Rather, TACAS UPS system 800 uses replaceable pressure tanks orcompressed air cylinders (e.g., a DOT cylinder), such as compressed aircylinder 802, in order to drive turbine 330.

As illustrated in FIG. 8, compressed air from compressed air cylinder802 is routed through turbine exhaust heat exchanger 712 prior to beingrouted through TSU 402 and into the inlet of turbine 330. Personsskilled in the art will appreciate that a primary advantage of TACAS UPSsystem 800 over the prior systems is that, as long as replacementcompressed air cylinders are available (e.g., to replace an exhaustedcompressed air cylinder 802), there will be an inexhaustible supply ofcompressed air to drive turbine 330. Accordingly, the availability ofcompressed air is not dependent on an external energy source (e.g.,utility power) or a fuel-combustion system.

FIG. 9 shows a TACAS UPS system 900 that is a slight variation withrespect to the type of heat recovery used in TACAS UPS system 700. TACASUPS system 900 includes a tank heat exchanger, or second TSU 902. TSU902 is made up of a tank of liquid (e.g., water) that is used to preheat cold compressed air from pressure tank 326. The liquid used by TSU902 is pumped by pump 904 through turbine exhaust heat exchanger 712 tocapture waste heat from exhaust 612 of turbine 330. Persons skilled inthe art will appreciate that instead of using the heat from the exhaustof turbine 330, an ambient air heat exchanger (not shown) or other typeof heat exchanger may be used to heat the liquid of TSU 902. It shouldalso be understood that if the energy gained from the exhaust of turbine330 is less than the energy used to pre-heat cold compressed air, theliquid's temperature (in TSU 902) will drop during the pre-heatingprocess. If, however, the energy gained from the exhaust of turbine 330is greater than the energy used to pre-heat cold compressed air, theliquid's temperature will rise during the pre-heating process.Therefore, additional compact and low cost heat exchangers may be addedto make up for any difference between the heat required for thepre-heating process and the heat drawn from the exhaust of turbine 330.Moreover, persons skilled in the art will appreciate that TSU 902 may beused for purposes other than pre-heating compressed air from pressuretank 326 before the compressed air is routed to TSU 402. For example,TSU 902 may be used solely to draw heat away from exhaust 612 (or indifferent applications where exhaust 612 is relatively cool compared tothe liquid of TSU 902, to cool the liquid of TSU 902). The invention isnot limited in this manner.

As shown in FIG. 9, TACAS UPS system 900 also includes an optional fan906 (which can operate at variable speeds) located near pressure tank326. Using fan 906, together with the remaining components describedabove, TACAS UPS system 900 provides an integrated source of backuppower and backup HVAC. If the temperature in the room or enclosure (notshown) containing TACAS UPS system 900 rises above a predeterminedlevel, for example, a controller (not shown) can make fan 906 spinfaster in order to transfer more of the relatively cool air surroundingpressure tank 326 throughout the room. Additionally, when thetemperature level is high, the controller can make pump 904 speed up theflow of the liquid from TSU 902 so that turbine exhaust heat exchanger712 absorbs more heat from turbine exhaust 612 and deposits the heatinto the tank of TSU 902.

Alternatively, if the temperature in the room drops below apredetermined level, for example, the controller (not shown) can slowdown the speed of fan 906 or stop it altogether. The controller can alsodecrease the flow rate of the liquid from TSU 902, so that less heatfrom turbine exhaust 612 is captured and stored in TSU 902. This, inturn, would compensate for temperatures that are too cold.

Persons skilled in the art will appreciate that TACAS UPS system 900 canprovide backup HVAC without using turbine exhaust heat exchanger 712 orTSU 902. For example, the UPS components alone, which give off heat, canbe used to heat the room, while fan 906 can be used to provide thecooling. Moreover, instead of or in conjunction with the use of fan 906to provide cooling, valve 328 can also be configured to release aportion of the compressed air from pressure tank 326 to provide directcooling of the room. This released air from pressure tank 326 can bedispersed throughout the room, or can be routed to a desired location toprovide isolated cooling within the room.

FIG. 10 shows another TACAS UPS system 1000 in accordance with theprinciples of the present invention which is identical to TACAS UPSsystem 900 of FIG. 9, except that TSU 402 has been removed. Accordingly,compressed air from pressure tank 326 is solely heated by heatexchangers 712 and 902 prior to being supplied to turbine 330. Whilethis configuration limits the ability to heat compressed air frompressure tank 326, the heat supplied from heat exchangers 712 and 902are often sufficient for this purpose. Accordingly, the removal of TSU402 may be desirable in order to result in less power being used topre-heat compressed air prior to entering the inlet of turbine 330 andto reduce the complexity of the system.

Moreover, although two specific heat exchangers are shown in TACAS UPSsystem 1000, the invention is not limited in this manner. Otherarrangements of heat exchangers as discussed herein may be used for thepurpose of pre-heating compressed air, absent TSU 402, without departingfrom the scope of the present invention.

FIG. 11 shows a TACAS UPS system 1100 that, while similar to TACAS UPSsystem 900, also includes additional heat exchangers 1102 and 1104 andadditional pump 1106. As illustrated in FIG. 11, these additional heatexchangers 1102 and 1104 are used in conjunction with heat exchanger 712(as described above). The invention, however, is not limited in thismanner.

In TACAS UPS system 1100, TSU 902 derives its thermal energy (inaddition to using heat exchanger 712) by using small heat exchangers1102 and 1104 that are respectively in thermal contact with compressor322 and pressure tank 326. In this manner, heat exchangers 1102 and 1104capture and store the waste heat given off during the air compressionprocess. Therefore, heat exchangers 902, 1102 and 1104, together, act asa compression process heat exchanger. Once the air compression processis complete, heat is stored in liquid form in TSU 902 in a thermallyinsulated reservoir. During discharge, the cold compressed air frompressure tank 326 is heated by TSU 902 (although not all three heatexchangers shown must be used) and then by main TSU 402 before beingrouted to turbine 330. In this configuration, for example, much of theheat lost during the compression process can be recaptured from heatstored in TSU 902.

FIG. 12 shows another TACAS UPS system 1200 configuration in accordancewith the principles of the present invention. The primary differencebetween TACAS UPS system 1200 and TACAS UPS system 700 is that TACAS UPSsystem 1200 includes heat exchanger 1202 (e.g., a waste energy heatexchanger or a solar energy heat exchanger) and ambient air heatexchanger 1204, instead of heat exchanger 712. Heat exchanger 1202pre-heats compressed air from pressure tank 326 before it is routed toTSU 402, but instead of using exhaust 612, uses either solar heat orwaste heat (e.g., from an industrial process) to further heat compressedair from pressure tank 326. In addition, TACAS UPS system 1200 utilizesambient air heat exchanger 1204 that uses heat from ambient air tofurther heat compressed air coming from pressure tank 326 prior to beingsupplied to TSU 402. Through this process, the surrounding ambient airis cooled at the same time that the cold compressed air from pressuretank 326 is heated. Persons skilled in the art will appreciate thatother types of ambient air heat exchangers may be used without departingfrom the scope of the present invention. For example, a simple fan (notshown) may be placed near pressure tank 326 which blows the cold airsurrounding pressure tank 326. Accordingly, any suitable type of ambientair heat exchanger may be used to maintain the temperature of the room(within which the TACAS UPS system or backup energy system is located)at an acceptable level by providing an appropriate level of coolingusing the cold compressed air in pressure tank 326. The invention is notlimited in this manner.

As with the previously described TACAS UPS systems and other backupenergy systems, the introduction of additional heat exchangers may addcost and complexity to the system, however, also increases systemefficiency and reduced the necessary amount of thermal storage materialin TSU 402 for a given energy output. It should also be noted thatalthough heat exchangers 1202 and 1204 are shown as pre-heating air frompressure tank 326 in a particular order, the invention is not limited inthis manner. Any combination of these or other types of heat exchangersdescribed in accordance with the principles of the present invention maybe used without limitation to a particular order in which the compressedair from pressure tank 326 is pre-heated. Moreover, moving the locationof a heat exchanger (such as ambient air heat exchanger 1204) couldprovide additional benefits.

FIG. 13 is a schematic diagram of a backup energy system 1300 forproviding backup power to critical electronics 220 while also providingbackup HVAC in accordance with the principles of the present invention.In backup energy system 1300, utility input 110 provides power tocritical electronics 220 during normal operating conditions. Backuppower is provided to critical electronics 220 by chemical battery bank230, through converter 231, and the TACAS components (as describedabove). It should be noted that instead of chemical battery bank 230, aflywheel or capacitor, for example, can be used to provide short termbackup power. Once utility input 110 fails, chemical battery bank 230and the TACAS components are used to ensure a continuous power feed tocritical electronics 220.

Meanwhile, backup energy system 1300 provides backup HVAC in thefollowing manner. Cold air from pressure tank 326 is routed through anambient air heat exchanger 250 (now located within housing 1302). As aresult, not only is cold air from pressure tank 326 pre-heated prior toentering TSU 402 (by the air from within housing 1302), but the airwithin housing 1302 is also cooled. If additional cooling is desired,the fan of ambient air heat exchanger 250 can be made to spin faster.Alternatively, if less cooling is desired, the fan of ambient air heatexchanger 250 can be slowed down.

It should be understood by those skilled in the art that it may bedesirable to provide DC power to critical electronics 220, in which caseconverter 231 is not necessary and additional converters may be added toconvert AC power from electric machine 332 and utility power 110 to DCpower to be supplied to critical electronics 220. The invention is notlimited in this manner.

FIG. 14 shows another backup energy system 1400 for providing backuppower to critical electronics 220 while also providing backup HVAC inaccordance with the principles of the present invention. Backup energysystem 1400 provides backup power to critical electronics 220 similarlyto the manner in which backup power is provided in backup energy system1300. In order to further control the temperature within housing 1402,however, backup energy system 1400 also includes bypass valve 1408,switches 1404 and 1406, and resistive circuits 1405 and 1407.

If the air within housing 1402 is too warm, relatively cool exhaust 612from turbine 330 can be used to directly cool the air inside (as shown),as opposed to diverting the exhaust 612 outside of housing 1402. Ifadditional cooling is required, switch 1406 can be closed, causingelectrical power from electrical machine 332 to be dissipated inresistive circuit 1407 (e.g., a resistor as shown) outside of housing1402 and thus making turbine exhaust 612 cooler. If maximum cooling isrequired, bypass valve 1408 can be completely opened so that cool airfrom pressure tank 326 is not heated by TSU 402 prior to passing throughturbine 330. To achieve intermediate levels of cooling, meanwhile, valve1408 can be adjusted to permit a desirable percentage of the air frompressure tank 326 to bypass TSU 402.

On the other hand, if the air inside housing 1402 is too cold, all ofthe air coming from pressure tank 326 can be optionally pre-heated byadditional heat exchangers (not shown) and then routed through TSU 402before being supplied to turbine 330. Additionally, switch 1404 can beclosed, causing the consumption of electrical power from electricalmachine 332 in resistive circuit 1405 (e.g., a resistor as shown) near acomponent that requires heat inside of enclosure 1402.

Although FIGS. 13 and 14 show two particular embodiments of energysystems providing backup power and HVAC, the present invention is notlimited in this manner. Additional heat exchangers or other components,as previously described, may be included without departing from thescope of the invention. Moreover, persons skilled in the art willappreciate that the principles of the present invention can be appliedto specific types of commercially available housing units (e.g., astandard computer rack) to provide different types of HVAC as desired.For example, a standard 19″ computer enclosure can be used with thebackup TACAS UPS and HVAC systems described above.

FIG. 15 shows a schematic diagram of a simplified backup HVAC system1500 in accordance with the principles of the present invention. Housing(or enclosure) 1502 can be any conventional type of housing (e.g., astandard computer enclosure as explained above) which holds criticalelectronics 220 or other components for which cooling is desired.

Housing 1502 shown in FIG. 15 connects to a purchased or rented pressuretank 802. Pressure tank 802 may be, for example, a replaceablecompressed air cylinder that is replaced with a tank full of compressedair once it has emptied. Alternatively, although not shown, pressuretank 802 may also use a compressor to produce compressed air which isstored in pressure tank 802.

Backup HVAC system 1500 also includes temperature measurement device1506. Device 1506, which may be any suitable device capable of sensingthe temperature inside of housing 1502 and conveying a signal based onthis temperature, sends a signal 1508 to controller 1504 once thetemperature inside housing 1502 rises above a predetermined level.Depending on signal 1508, controller 1504 opens valve 328 such that adesirable amount of cool air from pressure tank 802 flows into housing1502, thereby cooling critical electronics 220; chemical battery bank230 (or any other suitable type of energy storage system) and converter231. In this manner, as long as relatively cold compressed air isavailable, cooling may be provided to the components located insidehousing 1502 regardless of available power sources.

Persons skilled in the art will appreciate that the backup energysystems and TACAS UPS systems discussed above in accordance with theprinciples of the present invention may be combined to meet therequirements of a particular application. Accordingly, each of theconfigurations described herein can be modified so that functions of oneconfiguration are combined or interchanged with the functions of anotherconfiguration without departing from the scope of the present invention.For example, each of the embodiments described herein in accordance withthe principles of the present invention may utilize a compressor and apressure tank to store compressed air, or alternatively, a replaceablecompressed air cylinder may be used without departing from the scope ofthe present invention. Additionally, although a flywheel is used as thebridging energy system in several of the above described embodiments,other types of backup energy sources may be used (e.g., a bank ofchemical batteries) in any of the configurations.

FIG. 16 shows a three-dimensional embodiment of a TACAS UPS system 1600constructed in accordance with the principles of the present invention.TACAS UPS system 1600 includes main UPS cabinet 1610 and optionalcabinet 1670 (which, as further explained below, can be left out), bothof which are shown without the side panels to facilitate the viewing oftheir respective internal components. It should be understood thatcabinets 1610 and 1670 are each preferably enclosed by sheet metal oranother suitable material, with doors in the front to allow a user toreach the components located within the sheet metal.

Main UPS cabinet 1610 includes several components which together act toprovide uninterruptible power to a load (not shown). Main UPS cabinet1610 includes a UPS electronics unit 1620 (having a hinged door 1621 topermit easy access). UPS electronics unit 1620 is kept at a relativelycool temperature through the use of standard fans 1611. Additionally,fans 1611 may also be used to pull relatively warm ambient air oversmall pressure tanks 1660 (thus heating small pressure tanks 1660),thereby enhancing the efficiency of TACAS UPS system 1600. Moreover,although a particular number of fans are shown in FIG. 16, the number offans 1611 may be changed as desired without departing from the scope ofthe invention. Moreover, the control of fans 1611 may be automated(e.g., controlled by a temperature measurement device as describedabove) or may be controlled directly by a user. For greater cooling, thespeed of fans 1611 may be increased. Meanwhile, for reduced or nocooling, the speed of fans 1611 may be reduced or the fans may be shutdown.

Main UPS cabinet 1610 also includes an integrated turbine generator 1651which is driven by compressed air from small pressure tanks 1660 togenerate power as needed. Air from small pressure tanks 1660 is routedthrough manifold 1643 to valve 1641. When turbine generator 1651 is tosupply power, valve 1641 is opened to allow compressed air originatingfrom small pressure tanks 1660 to drive turbine generator 1651.Additionally, a compressor 1640 rests on top of compressor mount 1652,which preferably acts as a sound barrier to reduce noise emissions fromthe turbine generator 1651. Compressor 1640 is used to refill smallpressure tanks 1660 through valve 1641 and manifold 1643, and may bepowered by the primary power source or another suitable source of power.

In order to ensure continuous power to a load, UPS electronics unit 1620also uses another source of backup power to provide bridging energybetween the time a primary power source has failed and the time thatturbine generator 1651 beings supplying adequate power. In thisembodiment, the bridging energy is provided to UPS electronics unit 1620using a flywheel 1632 and a motor/generator 1631. When primary power isavailable, motor/generator 1631, which is acting as a motor, uses theprimary power to maintain the rotation of flywheel 1632. Once there isan interruption in the primary power source, controller electronics (notshown) within UPS electronics unit 1620 signals motor/generator to beginoperating as a generator, which is driven by the kinetic energy storedin flywheel 1631 is the form of rotational momentum. It should beunderstood that although a flywheel and a motor/generator are used inTACAS UPS system 1600 to provide bridging energy, the invention is notlimited in this manner. For example, a bank of chemical batteries couldbe used instead in order to provide the bridging energy necessary toensure continuous power is supplied to the load.

Main UPS cabinet 1610 does not include a TSU for pre-heating compressedair from small pressure tanks 1660 before the compressed air is routedto turbine generator 1651. Omitting a TSU results in less power outputavailability for a given volume and pressure of compressed air, however,is also results in main cabinet 1610 having lower cost and complexityand a faster response time (because air does not need to be routedthrough a TSU). It should be understood, however, that one or more TSU'smay be included in main UPS cabinet 1610 in accordance with theprinciples of the present invention.

Optional cabinet 1670 is used during prolonged outages of the primarypower source (e.g., if a long-term source of backup power is notavailable). As shown in FIG. 16, optional cabinet 1670 includessecondary pressure tanks 1680 and a TSU 1681. When secondary pressuretanks 1680 are used to drive turbine generator 1651 (either inconjunction with small pressure tanks 1660 or alone), air is routed fromsecondary pressure tanks 1680 through manifolds 1644 and 1645 and valve1647 and through TSU 1681. TSU 1681 may be, for example, steel which iskept at a relatively high temperature using an electric resistive heater(not shown). Additionally, insulation may be used to prevent heat frombeing released from TSU 1681 (as shown in FIG. 16). Once the compressedair coming from secondary pressure tanks 1680 has been heated by TSU1681, this heated air travels through pipe 1646 and T-connection 1642 todrive turbine generator 1651. It should be understood that T-connection1642 may be eliminated if optional cabinet 1670 is not being used, inwhich case compressed air from small pressure tanks 1660 would flowthrough valve 1641 and directly to turbine generator 1651 (instead ofthrough T-connection 1642 as currently shown).

Once secondary pressure tanks 1680 are depleted of compressed air, theymay be either replaced or refilled using compressor 1640. In the lattercase, air is supplied back via the same bi-directional route. (e.g.,through pipe 1646) to refill secondary pressure tanks 1680 withcompressed air. Control line 1648 carries control signals (e.g., throughan electrical wire) to, for example, open or close valves to allowproper routing of compressed air.

Furthermore, when optional cabinet 1670 is being used, exhaust air fromturbine generator 1651 may be used to pre-heat air to be heated by TSU1681. This is accomplished by routing exhaust air from turbine generator1651 through an exhaust pipe (not shown) to the grated bottom 1672 ofoptional cabinet 1670. This relatively hot exhaust air is then cooled asit flows up passed the relatively cold secondary pressure tanks 1680 andout vents 1671, thereby increasing runtime by heating secondary pressuretanks 1680 as they discharge.

Persons skilled in the art will appreciate that the features of thevarious embodiments described above in accordance with the principles ofthe present invention may also be incorporated into TACAS UPS system1600. For example, various heat exchangers may be included in main UPScabinet 1610. Moreover, relatively cold compressed air from smallpressure tanks 1660 or secondary pressure tanks 1680 may be releasedinto the air to provide cooling. Accordingly, TACAS UPS system 1600 mayprovide heating or cooling for components located within the systemitself, or for a room or other enclosure in which the system is located.The invention is not limited in this manner.

As also shown in FIG. 16, cabinets 1610 and 1670 are mounted on aconcrete slab 1691 using mounting cleats 1692. Nevertheless, alternativesupport may be provided to retain the positioning of cabinets 1310 and1370 without departing from the scope of the present invention.

FIG. 17 shows another three-dimensional embodiment of a TACAS UPS system1700 constructed in accordance with the principles of the presentinvention. TACAS UPS system 1700 is similar to TACAS UPS system 1600,except that additional optional cabinets 1670 have been added to providea longer runtime. In this manner, additional secondary pressure tanksfrom within additional optional cabinets 1670 may be used to driveturbine generator 1651 (as described above) when backup power is needed.The supplying of compressed air to turbine generator 1651 isaccomplished through the connection of the various pipes 1646 emergingfrom the multiple optional cabinets 1670. Moreover, compressor 1640 maybe used to refill the secondary pressure tanks 1680 located in each ofthe additional optional cabinets 1670 (as described above).

The above described embodiments of the present invention are presentedfor purposes of illustration and not of limitation, and the presentinvention is limited only by the claims which follow.

1. An apparatus comprising: a source of short-term backup power forproviding backup power to a critical load, the critical load locatedinside a housing, and the housing having an internal temperature; acompressed air reservoir for storing compressed air; at least one valvecoupled to the compressed air reservoir; an ambient air heat exchangercoupled to the at least one valve; a compressed air turbine coupled tothe at least one valve to receive the compressed air and release aturbine exhaust; and an electrical generator powered by the turbine, forproviding backup power to the critical load.
 2. The apparatus of claim1, wherein: the compressed air reservoir is a replaceable compressed airtank.
 3. The apparatus of claim 1, wherein: the ambient air heatexchanger includes at least one fan.
 4. The apparatus of claim 3,wherein: the fan is a variable-speed fan, the speed of the fan dependingon the internal temperature of the housing.
 5. The apparatus of claim 1,further comprising: a compressor coupled to the at least one valve forfilling the compressed air reservoir with compressed air; wherein thecompressor has a motor.
 6. The apparatus of claim 1, further comprising:at least one thermal storage unit coupled between the compressed airreservoir and the turbine to heat the compressed air.
 7. An apparatuscomprising: a source of short-term backup power for providing backuppower to a critical load, the critical load located inside a housing,and the housing having an internal temperature; a compressed airreservoir for storing compressed air; at least one valve coupled to thecompressed air reservoir; a compressed air turbine coupled to the atleast one valve to receive the compressed air and release a turbineexhaust into the housing; and an electrical generator powered by theturbine, for providing backup power to the critical load.
 8. Theapparatus of claim 7, wherein: the compressed air reservoir is areplaceable compressed air tank.
 9. The apparatus of claim 7, furthercomprising: a compressor coupled to the at least one valve for fillingthe compressed air reservoir with compressed air, wherein the compressorhas a motor.
 10. The apparatus of claim 7, further comprising: at leastone thermal storage unit coupled between the compressed air reservoirand the turbine to heat the compressed air.
 11. The apparatus of claim10, further comprising: a bypass valve for allowing at least a portionof the compressed air to bypass the at least one thermal storage unit.12. The apparatus of claim 7, further comprising: a resistive circuitlocated outside the housing and electrically coupled to the electricalgenerator, the resistive circuit selectively dissipating electricalpower from the electrical generator based on the internal temperature ofthe housing to lower the internal temperature of the housing.
 13. Theapparatus of claim 7, further comprising: a resistive circuit locatedinside the housing and electrically coupled to the electrical generator,the resistive circuit selectively dissipating electrical power from theelectrical generator based on the internal temperature of the housing toraise the internal temperature of the housing.
 14. An apparatuscomprising: a compressed air reservoir for storing compressed air; atleast one valve coupled to the compressed air reservoir; a compressedair turbine coupled to the at least one valve to receive the compressedair and release a turbine exhaust; an electrical generator powered bythe turbine, for providing backup power to a critical load locatedinside a housing, the housing having an internal temperature; and a fanassociated with the compressed air reservoir to move cool air from nearthe compressed air reservoir to lower the internal temperature of thehousing.
 15. The apparatus of claim 14, wherein: the compressed airreservoir is a replaceable compressed air tank.
 16. The apparatus ofclaim 14, further comprising: a compressor coupled to the at least onevalve for filling the compressed air reservoir with compressed air,wherein the compressor has a motor.
 17. The apparatus of claim 14,wherein: the fan is a variable-speed fan, the speed of the fan dependingon the internal temperature of the housing.
 18. The apparatus of claim14, wherein: the at least one valve is capable of releasing at least aportion of the compressed air into the housing based on the internaltemperature of the housing.
 19. The apparatus of claim 14, furthercomprising: a reservoir heat exchanger coupled between the compressedair reservoir and the turbine to heat the compressed air before itreaches the turbine.
 20. The apparatus of claim 19, further comprising:a turbine exhaust heat exchanger coupled to the turbine exhaust to coolthe turbine exhaust; and a pump coupled between the reservoir heatexchanger and the turbine exhaust heat exchanger.